1. Field of the Invention
This invention relates to engine generator sets and, more particularly, to engine generator sets with a more compact, modular design and improved cooling characteristics.
2. Description of the Relevant Art
The following descriptions and examples are provided as background only and are intended to reveal information that is believed to be of possible relevance to the present invention. No admission is necessarily intended, or should be construed, that any of the following information constitutes prior art impacting the patentable character of the subjected mater claimed herein.
An engine generator set (otherwise referred to as a “generator set” or “gen-set”) is the combination of an electrical generator and an engine (prime mover), which are mounted together to form a single piece of equipment. Engine generator sets are available in a wide range of power ratings, including small, portable units that can supply several hundred watts of power, hand-cart mounted units that can supply several thousand watts, and stationary or trailer-mounted units that can supply over a million watts. Regardless of the size, generator sets may run on a variety of different fuels, such as gasoline, diesel, natural gas, propane (liquid or gas), bio-diesel, sewage gas or hydrogen. Most of the smaller units are built to use gasoline as a fuel, while larger units typically use diesel, natural gas or propane.
Engine generator sets are often used to supply electrical power in places where utility power is not available, or where power is needed only temporarily or as a backup. Small generators are sometimes used to supply power tools at construction sites. Trailer-mounted generators supply power for temporary installations of lighting, sound amplification systems, amusement rides, etc., and may also be used for emergencies or backup where either a redundant system is required or no generator is on site.
Standby power generators are permanently installed at an installation site and are generally kept ready to supply power during temporary interruptions of the utility power supply. Hospitals, communications service installations, data processing centers, sewage pumping stations and many other important facilities are often equipped with standby power generators, as well as some businesses and residences. Some standby power generators can automatically detect the loss of grid power, start the engine, run using fuel from a natural gas line, detect when grid power is restored, and then turn itself off—with no human interaction.
Engine generator sets utilized for standby power generation can provide anywhere from about 6 kW to about 3250 kW or more of single phase or three phase power at a variety of different output voltages and frequencies. As shown in FIG. 1, the main components of an engine generator set include an internal combustion engine 1, electrical generator 2, fuel system 3, voltage regulator 4, cooling and exhaust systems 5, lubricating systems 6, battery charger 7 and control panel 8. These components are typically mounted on the generator's skid base (or main assembly/frame) 9 and enclosed within a generator set housing or enclosure (not shown in FIG. 1).
The internal combustion engine 1 provides a mechanical energy input to the electrical generator or alternator 2, which converts the mechanical energy into an electrical output. The size of the engine is directly proportional to the maximum power output the generator can supply. As noted above, the engine may run on a variety of different fuels, such as gasoline, diesel, natural gas, propane, etc. In the case of smaller engine generator units, the fuel system 3 may include a fuel tank, which is mounted to the generator's skid base or on top of the generator frame 9. For commercial applications, it may be necessary to erect and install an external fuel tank, or provide a connection to a utility gas line. The lubricating system 6 provides lubricants to the moving parts of the engine.
In generator sets used for standby power generation, the engine crank shaft is typically coupled to the electrical generator 2 along a horizontal axis. The electrical generator 2 is typically a high efficiency alternator having a rotor coupled to the engine crank shaft and a stator coupled for supplying alternating current to an electronic control section, which controls operation of the alternator and internal combustion engine. The voltage regulator 4 regulates the AC voltage produced by the alternator 2 by determining whether and by how much the sensed voltage/current deviates from desired values.
During operation, heat is produced by both the engine 1 and the alternator 2 and this heat must be removed from the enclosure for proper system operation. Heat may be removed by a variety of different cooling and exhaust systems 5, including both air and liquid cooling systems. One conventional solution for removal of heat is to provide separate mechanically driven fans for the engine 1 and the alternator 2. In a horizontally shafted engine 1, the engine crank shaft is coupled at one end to the rotor of the alternator 2, and at an opposite end to a fan 5 mounted within a sidewall of the generator set housing. The fan is driven by the engine crank shaft to blow cooling air over the engine. In many cases, a second fan (not shown in FIG. 1) may be coupled to the engine crank shaft between the engine 1 and the alternator 2 to cool the rotor windings and provide additional engine cooling. Because these fans are both driven by the engine crank shaft, they only provide cooling when the engine is running. These mechanically driven fans are also very noisy and inefficient, since fan speed is directly related to engine speed and cannot be optimized for temperature.
In some cases, the generator set may also include an electronic control section including a control panel, a controller, and one or more output sensors and electrical circuit breaker(s). The output of the alternator 2 may be fed through the output sensors and the electrical circuit breaker(s) to the output lines of the generator set. The controller is typically a microcomputer based subsystem that executes a control program to govern the operation of the alternator 2. The controller may receive signals from the control panel 8 and the output sensors, which sense the voltage and current levels of the electricity produced by the alternator, and from those signals may derive the frequency and polarity of the AC current and voltage produced by the alternator. The electrical circuit breaker(s) may operate to open and close a set of contacts that connect the output lines of the generator set to an electrical distribution system or customer load.
In some cases, a number of generator sets may be coupled in parallel as energy sources in what is called a “paralleling system.” In a paralleling system, the output lines of each generator set are typically coupled to a three-phase parallel electrical bus having three separate conductors. In some cases, parallel electrical bus may be connected through a main distribution panel to various loads within a structure (such as a building or residence), a campus or other facility. The main distribution panel typically includes a single, large transformer for transforming the AC voltage (e.g., 480V) output from all parallel-coupled generator sets to a substantially higher voltage (e.g., 12,470 V), which can be supplied to the loads. Unfortunately, using a single, large transformer at the main distribution panel presents a single point of failure to the paralleling system. In addition, a single large transformer also requires larger inrush currents when energized, and therefore, limits the number that can be energized at once from a single generator set.
In other cases, the parallel electrical bus may be coupled to utility power lines by an automatic transfer switch (ATS), which detects when electricity from the utility lines is interrupted and disconnects the parallel electrical bus from the utility lines in response. In such cases, the parallel-coupled generator sets can export power and energy to the utility grid if: (a) suitable transformers are provided to allow the voltages produced by the generator sets to be stepped up to a voltage that is equivalent to the delivery voltage of the local utility grid, and (b) additional control equipment is provided to allow the waveforms of the electricity produced by the generator sets to be synchronized with those of the utility. In order to parallel synchronously to the utility lines, the AC voltages output from the parallel-coupled generator sets must be stepped up to voltages ranging from about 2,400-38,000 volts by a transformer with sufficient capacity to export the entire capacity of the group of paralleled generator sets. However, using a single, large transformer for such purpose has many disadvantages, as noted above.
In addition to the problems associated with using a single, large transformer to transform the AC voltage output from the parallel-coupled generator sets, the large output current generated by each generator set requires relatively large and expensive cables to be used to connect the output from each generator set to the parallel electrical bus. For example, a generator set configured to provide three phase AC voltage of 480/277V at approximately 350 KW generates approximately 585 A of AC current per phase. At these output current levels, two sets of large 500MCM cables are required per phase and neutral, which results in 8 large wires. Another disadvantage of connecting the generator set output lines to the transformer at the main distribution panel is that long runs of 500MCM cables are subject to losses from the resistance of the wires to large current flow.
As noted above, the components of each generator set are typically enclosed within a generator set housing or enclosure. In many cases, the generator set housing is substantially rectangular in shape, and because of the horizontal arrangement of components (see, FIG. 1), the generator set housing is often significantly greater in length than in width and height. Particular dimensions of conventional generator set housings vary greatly for different power ratings and configurations, although it is safe to say that generator sets with larger power ratings generally have larger footprints. For example, the length of a smaller generator set providing only 6 kW of power may be as little as 3-5 feet, whereas a larger generator set providing about 350 kW of power may be about 15-20 feet in length. It is easy to recognize how real estate is quickly consumed when a number of larger generator sets are coupled together in a paralleling system.